FLASH is a light source directly coupled to a superconducting linear accelerator operated at 2.2 Kelvin. As the whole vacuum system from the FEL to the experiment will be operated without windows there are special requirements on the optics and the vacuum system of the beamline and of the user experiments. Hydrocarbons and dust are expected to degrade the performance of the FEL and the quality of the photon beam and must therefore be kept on a minimum level. FLASH staff will supply an interface between the beamline and the experiment to keep the right vacuum conditions in the beamline. To make sure that the experimental end station fits to the requirements of the interface please, get in touch with your local contact already in an early stage of a planned project.